在編寫匯出功能使用action請求，在處理匯出異常時期望跳轉異常頁，Controller中的方法返回型別String的url

在處理完邏輯匯出檔案後後臺控制檯出現

WARN  [org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver] (default task-22) Handling of [org.springframework.http.converter.HttpMessageNotWritableException] resulted in Exception: java.lang.IllegalStateException: UT010019: Response already commited

and

ERROR [io.undertow.request] (default task-22) UT005023: Exception handling request to /snq-admin/data/exportDataDetail.do: org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: UT010029: Stream is closed; nested exception is java.io.IOException: UT010029: Stream is closed

Caused by: org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: UT010029: Stream is closed; nested exception is java.io.IOException: UT010029: Stream is closed

Caused by: java.io.IOException: UT010029: Stream is closed

在寫入檔案時呼叫requestOutputStream.write()方法已將response發出，再在Controller中return時被認為是再發送一次，因而會報錯，解決這個問題只需返回null即可。